The present invention relates to an optical image recording system and an associated processing system.
1. The Technical Field
Optical image recording systems such as conventional cameras and electronic cameras are available in many different designs and sizes.
Portable cameras are usually miniaturized for the purpose of being portable in a bag or pocket. A general problem of such portable cameras is that their sizes and shapes make them unpractical and unhandy to carry along as can be done with personal equipment of sizes such as a credit card or drivers licence.
Electronic cameras are also available in different designs for various applications such as built-in cameras in permanent installations or as portable cameras. Such electronic cameras are usually designed on one or more printed circuit boards (PCB) for which a minimum dimension in the two directions of the plane is required. The height of the camera is usually dependent on the dimensions of the lens system used, and it is totally dependant on the focal length thereof.
A disadvantage of these image recording systems is that they are difficult to miniaturize.
Prior art lens systems for such cameras are often miniaturized by the use of a limited number of lenses so that the effective lens height thereof can be brought down to approximately 1 times the focal length of the lens system.
A consequence of using only a few, typically only one lens, is that the formed image has an unsatisfactory resolution and performance. Therefore, in order to achieve a reasonable resolution, it is necessary to reduce the aperture whereby, however, the photosensitivity is reduced.
Further, if a low height is to be maintained, only a short focal length—and consequently a wide angle field of view—can be used. Any increase in the focal length of the lens will lead to an increase of the height.
Especially for electronic cameras a further disadvantage is that the transfer of the recorded optical information requires the use of cumbersome external cables connecting the camera and image processing system, or it requires an exchangeable memory such as a diskette or a solid state memory. For the latter two data carriers, the cumbersome cables can be avoided, but they will require the software for controlling the image processing system to be loaded on the data carrier which requires space thereon.
2. Prior Art
JP 01-176 168 discloses a compact electronic still camera comprising a camera main body in form of a plastic resin card having a thickness within 10 mm. The card camera comprises a CCD 2-dimensional image sensor and a semiconductor memory for electronic recording of an image, and a connector for the connection of the circuit inside the card camera with the circuit of an image reproducing device for transferring the still picture information thereto. The camera is provided with a demountable lens to be removed when the card camera must be flat.
DE 26 59 729 discloses a single lens reflex pocket camera having a twice 90 degrees broken optical axis to accommodate a built in zoom lens. The camera receives the optical information through a side of the camera body. Such a system has the disadvantage that when the body height is low, the viewfinder is not properly framed, i.e. it is difficult to look through it and see the object. For a camera with a very low body height, it is impossible to look through the viewfinder. Furthermore, a down scaling of the disclosed optical system requires very small and thin lenses which are very difficult to manufacture within small tolerances with present technology and which are impractical to handle. For an image recording system that should be mounted flat on a wall, e.g. as part of a door phone, it cannot be allowed that the optical information is received through a side of the camera body.
DE 25 53 395 discloses an endoscope objective comprising an inverted telephoto objective connected to a waveguide. The endoscope neither comprises a body having a configuration with a low height and with broad surfaces, nor does it comprise an optical image recording system with image recording device, viewfinder, and a solid state memory. The endoscope objective cannot be accommodated in the body of an image recording system having an S-ratio less than 1.9, i.e. having a large diagonal of the image recording device as compared to the height of the body of the image recording system, nor can a high resolution image recording system based on the endoscope objective be incorporated in such a body having a size to be kept in a wallet or in the form of a type II PCMCIA card.
JP 63-199 312 discloses an electronic camera intended for small image sizes and short focal lengths. The camera uses a non-folded lens system having a long back focus allowing space for a blur filter to be incorporated therein. Very thin lenses are required, which is not desirable from a practical point of view as the lenses become very vulnerable and sensitive to variations in lens thickness. It is impossible to effectively minimize the effective lens height. Hence, a very compact high resolution camera cannot be made.
EP 0 676 663 discloses a compact camera which is suitable for use as hidden or candid camera. The lens section is fabricated to minimize the thickness of the camera. In an embodiment, the camera includes a plane body having a pinhole disposed therein and a lens disposed on the plane body. Only short focal lengths can be accepted in order to maintain a flat body. The lens is a single element aspherical lens which results in a low resolution and limited speed which is not acceptable for high resolution applications. Furthermore, the back focus is too short to provide enough space for colour filters comprising multiple birefringent plates to be inserted between the lens and the CCD. Hence, for high resolution applications aliasing might occur.